Simulate visibilities

vis-simulate effectively turns a sky-model source list into visibilities.

Simple example

hyperdrive vis-simulate \
    -s srclist.yaml \
    -m *.metafits

Considerations

Disabling beam attenuation

--no-beam

Dead dipoles

By default, dead dipoles in the metafits are used. These will affect the generated visibilities. You can disable them with --unity-dipole-gains.

Vetoing

Vetoing removes sources that have components below the elevation limit, components that are too far from the phase centre, components with beam-attenuated flux densities less than the threshold, and/or remove sources that aren't in the top N sources specified by num_sources.

This is important for calibration, because it is expensive to generate a sky model, and using only dim sources would result in poor calibration.

Sources are vetoed if any of their components are further away from the phase centre than source_dist_cutoff_deg or their beam attenuated flux densities are less than veto_threshold.

Source-list vetoing can do unexpected things. You can effectively disable it by supplying --veto-threshold 0, although the veto routine will still:

  1. Remove sources below the horizon; and
  2. Sort the remaining sources by brightness based off of the centre frequencies MWA coarse channels.

If there are fewer sources than that of num_sources, an error is returned; it's up to the caller to handle this if they want to.

The frequencies to use for beam calculations are the coarse channel centers, 1.28 MHz apart on MWA.